The present invention relates to typewriters, and more particularly to a ribbon feed mechanism operable to incrementally feed a ribbon in response to actuating a printing mechanism and in response to shifting a carriage from an upper case position to a lower case position.
In typewriters which shift a carriage from a lower to an upper case position for printing upper case characters, a ribbon vibrator lifts a ribbon to a first elevation. When a printing mechanism is actuated, the ribbon vibrator lifts the ribbon to a second elevation higher than the first elevation for printing an upper case character. When the ribbon is supported on an arm which is pivotally supported on a ribbon cartridge, the printing character strikes the ribbon at an angle relative to the length of the ribbon expending that area of the ribbon. This expended area of the ribbon can overlap the next printed character when the carriage is returned for printing a lower case character. When a fabric ribbon is used, an overlapping of printing characters does not noticably affect the density of the printed characters. However, when a carbon ribbon is used, overlapping of printed characters omits printing, which is highly undesirable.
This problem could be avoided by having the printing mechanism feed the carbon ribbon with larger increments than necessary for normal printing. Feeding larger increments would be undesirable since the carbon ribbon, which is fed past the print point only once, would be inefficiently used.
The present invention avoids the problem of overlap printing and maintains efficient use of the carbon ribbon by feeding the ribbon one additional increment when actuating a carriage shift mechanism to return the carriage from the upper case position to the lower case position.